Table 1.
Selected epidemiologic factors and EOC risk by histotype in three ovarian cancer consortia: Ovarian Cancer Cohort Consortium (OC3), Ovarian Cancer Association Consortium (OCAC) and the Collaborative Group on Epidemiological Studies of Ovarian Cancer
| Risk Factors | Serous | Endometrioid | Clear Cell | Mucinous | ||||
|---|---|---|---|---|---|---|---|---|
| Direction of Associatio n |
RR or OR (95% CI)a |
Direction of Associatio n |
RR or OR (95% CI)a |
Direction of Associatio n |
RR or OR (95% CI)a |
Direction of Associatio n |
RR or OR (95% CI)a |
|
| Cigarette smoking (Current vs. never smokers) [44,47,48] | Null | 0.99 (0.94–1.05) | Modest Inverse | 0.93 (0.79–1.09) | Modest Inverse | 0.95 (0.74–1.21)b | Positive | 1.27 (1.01–1.59) |
| 0.89 (0.76–1.04) | 0.84 (0.69–1.02) | 0.74 (0.56–0.98) | 1.31 (1.03–1.65) | |||||
| 0.99 (0.91–1.08) | 0.81 (0.70–0.94) | 0.80 (0.63–1.01) | 1.79 (1.47–2.17) | |||||
| Tubal ligation [43,47,53] | Weak Inverse | 0.91 (0.79–1.06) | Strong Inverse | 0.60 (0.41–0.88) | Strong Inverse | 0.35 (0.18–0.69) | Inconsistent | 1.01 (0.60–1.71) |
| 0.81 (0.74–0.89) | 0.48 (0.40–0.59) | 0.52 (0.40–0.67) | 0.68 (0.52–0.89) | |||||
| 0.84 (0.77–0.92) | 0.54 (0.43–0.69) | 0.55 (0.39–0.77) | 0.99 (0.84–1.18) | |||||
| BMI (Per 5 kg/m2 increase) [45,47,50] | Null | 0.97 (0.93–1.01) | Positive | 1.07 (0.99–1.16) | Null | 1.04 (0.92–1.17) | Positive | 1.08 (0.96–1.20) |
| 0.98 (0.94–1.02) | 1.17 (1.11–1.23) | 1.06 (0.96–1.17) | 1.19 (1.06–1.32) | |||||
| 1.00 (0.96–1.04) | 1.07 (1.01–1.13) | 1.05 (0.95–1.15) | 1.15 (1.07–1.23) | |||||
| Endometriosis [26,47] | Null (High- grade)c | 1.11 (0.70–1.74) | Positive | 2.32 (1.36–3.95) | Positive | 2.87 (1.53–5.39) | Null | 1.62 (0.58–4.51) |
| 1.13 (0.97–1.32) | 2.04 (1.67–2.48) | 3.05 (2.43–3.84) | 1.02 (0.69–1.50) | |||||
| N/A | N/A | N/A | N/A | |||||
| Estrogen-only hormone therapy (Ever vs. never use) [46,49] | Positive | N/Ad | Positive | N/Ad | Null | N/Ad | Null | N/Ad |
| 1.57 (1.23–2.00) | 1.82 (1.10–3.03) | 0.80 (0.38–1.68) | 0.80 (0.38–1.69) | |||||
| 1.59 (1.45–1.75) | 1.42 (1.19–1.69) | 0.88 (0.71–1.10) | 0.91 (0.66–1.24) | |||||
| Oral contraceptive use (Duration per 5-year increase of use) [47,51] | Inverse | 0.85 (0.81–0.89) | Inverse | 0.86 (0.77–0.95) | Inverse | 0.86 (0.74–1.00) | Null | 1.02 (0.80–1.31) |
| N/A | N/A | N/A | N/A | |||||
| 22.1% (SE 2.9) reduction in risk | 27.1% (SE 4.8) reduction in risk | 21.3% (SE 7.3) reduction in risk | 6.7% (SE 5.8) reduction in risk | |||||
| Parity (Per term pregnancy) [47,52] | Weak Inverse | 0.93 (0.92–0.95) | Inverse | 0.78 (0.74–0.83) | Strong Inverse | 0.68 (0.61–0.76) | Weak Inverse | 0.91 (0.84–0.99) |
| N/A | N/A | N/A | N/A | |||||
| 0.87 (0.83–0.91) | 0.72 (0.66–0.77) | 0.56 (0.49–0.65) | 0.85 (0.77–0.93) | |||||
| Breastfeeding Duration (Per year for OC3 and per month for the Collaborative Group) [47,52] | Inverse | 0.94 (0.86–1.03) | Inverse | 0.85 (0.69–1.05) | Null | 1.03 (0.81–1.33) | Inverse | 0.88 (0.63–1.23) |
| N/A | N/A | N/A | N/A | |||||
| 0.98 (0.97–0.99) | 0.98 (0.98–1.00) | 1.00 (0.97–1.03) | 0.97 (0.95–1.00) | |||||
RR: relative risk, OR: odds ratio, CI: confidence interval, SE: standard error, N/A: not applicable
The order of the RRs from top to bottom is OC3, OCAC, and the Collaborative Group on Epidemiological Studies of Ovarian Cancer. For tubal ligation, the Million Women Study was included instead of the Collaborative Group. For parity and breastfeeding, a pooled analysis of nine studies in the Collaborative Group was used instead of the full set of studies in the Collaborative Group on Epidemiological Studies of Ovarian Cancer.
Although cigarette smoking overall was not associated with risk of clear cell ovarian cancer in OC3, an inverse association was observed for pack-years (Per 20 pack-years: RR=0.68, 95% CI=0.53–0.89).
Among LGSC, a strong positive association was observed for women with a history of endometriosis (OC3: RR=3.77, 95% CI=1.24–11.48; OCAC: OR=2.11, 95% CI=1.39–3.20).
OC3 evaluated hormone therapy use overall but not by type of therapy.